Spatial association between the locations of roots and water flow paths in highly structured soil

Considerable evidence exists that the majority of low tension water flow through highly structured clayey soil occurs in a small fraction of total pore space and that the flow paths converge as depth increases. In structured clayey soils, water tends to flow in locations where macroporosity is high and roots tend to enjoy this condition as well. Water reduces the strength and mechanical impedance of the soil. Mechanical impedance of clayey soils tends to be extremely high when the soils are dry so one might expect that there would be a positive spatial correlation between the location of roots and the location of water flow paths in highly structured clayey soils. Understanding the relationship between the location of roots in soil relative to the location of water flow paths is important in understanding how plants obtain nutrients and water for growth, and it would also be of considerable importance in phytoremediation research and research into the prevention of groundwater contamination. This experiment was designed to map the locations of flow paths and roots and then measure the spatial association of the two.
A pasture on Ship?s clay along the Brazos River was chosen as the research site. Three plots were irrigated with an Erioglaucine dye solution used to stain flow paths.
After irrigation the soil was excavated to a depth of 25 cm. On the resulting horizontal plane the dye stain pattern was mapped using photography. The locations of roots were mapped on clear plastic sheets. During mapping the roots were categorized by size. The mapping procedure was repeated at depth of 45 cm and 75 cm for all plots. The root maps were overlaid on the photographic images and analyzed for a spatial association. There was no evidence the smallest (> 1 mm diameter) roots were not randomly distributed. The results did show that the larger roots were not randomly distributed, and evidence pointed to a clustering of roots in and around the dye stained flow paths. However, the data fell short of establishing a spatial association. The lack of more conclusive data was likely the result of inaccuracies in the mapping.